Showing papers by "University of Chicago published in 2004"
TL;DR: In this article, the authors randomly generate placebo laws in state-level data on female wages from the Current Population Survey and use OLS to compute the DD estimate of its "effect" as well as the standard error of this estimate.
Abstract: Most papers that employ Differences-in-Differences estimation (DD) use many years of data and focus on serially correlated outcomes but ignore that the resulting standard errors are inconsistent. To illustrate the severity of this issue, we randomly generate placebo laws in state-level data on female wages from the Current Population Survey. For each law, we use OLS to compute the DD estimate of its “effect” as well as the standard error of this estimate. These conventional DD standard errors severely understate the standard deviation of the estimators: we find an “effect” significant at the 5 percent level for up to 45 percent of the placebo interventions. We use Monte Carlo simulations to investigate how well existing methods help solve this problem. Econometric corrections that place a specific parametric form on the time-series process do not perform well. Bootstrap (taking into account the autocorrelation of the data) works well when the number of states is large enough. Two corrections based on asymptotic approximation of the variance-covariance matrix work well for moderate numbers of states and one correction that collapses the time series information into a “pre”- and “post”-period and explicitly takes into account the effective sample size works well even for small numbers of states.
9,397 citations
TL;DR: In this article, the authors outline the mechanism by which brokerage provides social capital, and show that between-group brokers are more likely to express ideas, less likely to have ideas dismissed, and more likely have ideas evaluated as valuable.
Abstract: This article outlines the mechanism by which brokerage provides social capital. Opinion and behavior are more homogeneous within than between groups, so people connected across groups are more familiar with alternative ways of thinking and behaving. Brokerage across the structural holes between groups provides a vision of options otherwise unseen, which is the mechanism by which brokerage becomes social capital. I review evidence consistent with the hypothesis, then look at the networks around managers in a large American electronics company. The organization is rife with structural holes, and brokerage has its expected correlates. Compensation, positive performance evaluations, promotions, and good ideas are disproportionately in the hands of people whose networks span structural holes. The between-group brokers are more likely to express ideas, less likely to have ideas dismissed, and more likely to have ideas evaluated as valuable. I close with implications for creativity and structural change.
4,442 citations
University of Texas at Austin1, University of California, Davis2, University of Montpellier3, Florida State University4, University of Chicago5, Washington University in St. Louis6, University of California, Berkeley7, University of Florida8, University of British Columbia9, University of York10, PSL Research University11, McGill University12
TL;DR: This framework is used to discuss why the metacommunity concept is useful in modifying existing ecological thinking and illustrate this with a number of both theoretical and empirical examples.
Abstract: The metacommunity concept is an important way to think about linkages between different spatial scales in ecology. Here we review current understanding about this concept. We first investigate issues related to its definition as a set of local communities that are linked by dispersal of multiple potentially interacting species. We then identify four paradigms for metacommunities: the patch-dynamic view, the species-sorting view, the mass effects view and the neutral view, that each emphasizes different processes of potential importance in metacommunities. These have somewhat distinct intellectual histories and we discuss elements related to their potential future synthesis. We then use this framework to discuss why the concept is useful in modifying existing ecological thinking and illustrate this with a number of both theoretical and empirical examples. As ecologists strive to understand increasingly complex mechanisms and strive to work across multiple scales of spatio-temporal organization, concepts like the metacommunity can provide important insights that frequently contrast with those that would be obtained with more conventional approaches based on local communities alone.
4,266 citations
University of Pennsylvania1, Massachusetts Institute of Technology2, Princeton University3, New York University4, Los Alamos National Laboratory5, University of Chicago6, Fermilab7, Ohio State University8, University of Arizona9, Drexel University10, Johns Hopkins University11, University of Pittsburgh12, Carnegie Mellon University13, New Mexico State University14, Spanish National Research Council15, University of Sussex16, University of Tokyo17, United States Department of the Navy18, University of Michigan19, Rochester Institute of Technology20, Pennsylvania State University21
TL;DR: In this paper, the authors measured cosmological parameters using the three-dimensional power spectrum P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in combination with WMAP and other data.
Abstract: We measure cosmological parameters using the three-dimensional power spectrum P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in combination with WMAP and other data. Our results are consistent with a "vanilla" flat adiabaticCDM model without tilt (ns = 1), running tilt, tensor modes or massive neutrinos. Adding SDSS information more than halves the WMAP-only error bars on some parameters, tightening 1� constraints on the Hubble parameter from h � 0.74 +0.18 −0.07 to h � 0.70 +0.04 −0.03, on the matter density from m � 0.25 ± 0.10 to m � 0.30 ± 0.04 (1�) and on neutrino masses from < 11 eV to < 0.6 eV (95%). SDSS helps even more when dropping prior assumptions about curvature, neutrinos, tensor modes and the equation of state. Our results are in substantial agreement with the joint analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive consistency check with independent redshift survey data and analysis techniques. In this paper, we place particular emphasis on clarifying the physical origin of the constraints, i.e., what we do and do not know when using different data sets and prior assumptions. For instance, dropping the assumption that space is perfectly flat, the WMAP-only constraint on the measured age of the Universe tightens from t0 � 16.3 +2.3
3,938 citations
TL;DR: Recommendations are reviewed for ongoing research that will more comprehensively expand understanding of the stigma-care seeking link and implications for the development of antistigma programs that might promote care seeking and participation are reviewed.
Abstract: Many people who would benefit from mental health services opt not to pursue them or fail to fully participate once they have begun. One of the reasons for this disconnect is stigma; namely, to avoid the label of mental illness and the harm it brings, people decide not to seek or fully participate in care. Stigma yields 2 kinds of harm that may impede treatment participation: It diminishes self-esteem and robs people of social opportunities. Given the existing literature in this area, recommendations are reviewed for ongoing research that will more comprehensively expand understanding of the stigma-care seeking link. Implications for the development of antistigma programs that might promote care seeking and participation are also reviewed.
2,975 citations
TL;DR: The authors study race in the labor market by sending fictitious resumes to help-wanted ads in Boston and Chicago newspapers and find that white names receive 50 percent more callbacks for interviews than African-Americans.
Abstract: We study race in the labor market by sending fictitious resumes to help-wanted ads in Boston and Chicago newspapers. To manipulate perceived race, resumes are randomly assigned African-American- or White-sounding names. White names receive 50 percent more callbacks for interviews. Callbacks are also more responsive to resume quality for White names than for African-American ones. The racial gap is uniform across occupation, industry, and employer size. We also find little evidence that employers are inferring social class from the names. Differential treatment by race still appears to still be prominent in the U.S. labor market. (JEL J71, J64).
2,890 citations
TL;DR: A draft genome sequence of the red jungle fowl, Gallus gallus, provides a new perspective on vertebrate genome evolution, while also improving the annotation of mammalian genomes.
Abstract: We present here a draft genome sequence of the red jungle fowl, Gallus gallus. Because the chicken is a modern descendant of the dinosaurs and the first non-mammalian amniote to have its genome sequenced, the draft sequence of its genome--composed of approximately one billion base pairs of sequence and an estimated 20,000-23,000 genes--provides a new perspective on vertebrate genome evolution, while also improving the annotation of mammalian genomes. For example, the evolutionary distance between chicken and human provides high specificity in detecting functional elements, both non-coding and coding. Notably, many conserved non-coding sequences are far from genes and cannot be assigned to defined functional classes. In coding regions the evolutionary dynamics of protein domains and orthologous groups illustrate processes that distinguish the lineages leading to birds and mammals. The distinctive properties of avian microchromosomes, together with the inferred patterns of conserved synteny, provide additional insights into vertebrate chromosome architecture.
2,579 citations
TL;DR: A short loneliness scale developed specifically for use on a telephone survey is described, finding that objective and subjective isolation are related, indicating that the quantitative and qualitative aspects of social relationships are distinct.
Abstract: Most studies of social relationships in later life focus on the amount of social contact, not on individuals' perceptions of social isolation. However, loneliness is likely to be an important aspect of aging. A major limiting factor in studying loneliness has been the lack of a measure suitable for large-scale social surveys. This article describes a short loneliness scale developed specifically for use on a telephone survey. The scale has three items and a simplified set of response categories but appears to measure overall loneliness quite well. The authors also document the relationship between loneliness and several commonly used measures of objective social isolation. As expected, they find that objective and subjective isolation are related. However, the relationship is relatively modest, indicating that the quantitative and qualitative aspects of social relationships are distinct. This result suggests the importance of studying both dimensions of social relationships in the aging process.
2,513 citations
TL;DR: In this article, it was shown that cosmic acceleration can arise due to very tiny corrections to the usual gravitational action of general relativity, of the form{R}^{\ensuremath{-}n}$ with $ng0.$.
Abstract: We show that cosmic acceleration can arise due to very tiny corrections to the usual gravitational action of general relativity, of the form ${R}^{\ensuremath{-}n}$ with $ng0.$ This model eliminates the need for a nonzero cosmological constant or any other form of dark energy, attributing a purely gravitational origin to the acceleration of the universe.
2,271 citations
TL;DR: In this study, 12 young, healthy, normal-weight men exhibited reductions in the satiety hormone leptin, increases in the hunger hormone ghrelin, and increases in hunger after 2 nights of only 4 hours of sleep compared with after two nights of 10 hours ofSleep, suggesting inadequate sleep seems to influence the hormones that regulate satiety and hunger.
Abstract: Sleep-deprived healthy persons experience increased hunger. They also have increased blood levels of leptin and decreased levels of ghrelin (hormones that regulate satiety and hunger). These hormon...
2,178 citations
TL;DR: In this article, private benefits of control in 39 countries using 393 controlling blocks sales are estimated and found to be associated with less developed capital markets, more concentrated ownership, and more privately negotiated privatizations.
Abstract: We estimate private benefits of control in 39 countries using 393 controlling blocks sales. On average the value of control is 14 percent, but in some countries can be as low as ‐4 percent, in others as high a +65 percent. As predicted by theory, higher private benefits of control are associated with less developed capital markets, more concentrated ownership, and more privately negotiated privatizations. We also analyze what institutions are most important in curbing private benefits. We find evidence for both legal and extra-legal mechanisms. In a multivariate analysis, however, media pressure and tax enforcement seem to be the dominating factors. THE BENEFITS OF CONTROL OVER corporate resources play a central role in modern thinking about finance and corporate governance. From a modeling device (Grossman and Hart (1980)) the idea of private benefits of control has become a centerpiece of the recent literature in corporate finance, both theoretical and empirical. In fact, the main focus of the literature on investor protection and its role in the development of financial markets (La Porta, Lopez-de-Salines, and Shleifer (2000)) is on the amount of private benefits that controlling shareholders extract from companies they run. In spite of the importance of this concept, there are remarkably few estimates of how big these private benefits are, even fewer attempts to document empirically what determines their size, and no direct evidence of their impact on financial development. All of the evidence on this latter point is indirect, based on the (reasonable) assumption that better protection of minority shareholders is correlated with higher financial development via its curbing of private benefits of control (La Porta et al. (1997)). The lack of evidence is no accident. By their very nature, private benefits of control are difficult to observe and even more difficult to quantify in a reliable
TL;DR: In this article, the authors identify the effect of social capital on financial development by exploiting social capital differences within Italy and find that households are more likely to use checks, invest less in cash and more in stock, have higher access to institutional credit, and make less use of informal credit.
Abstract: To identify the effect of social capital on financial development, we exploit social capital differences within Italy. In high-social-capital areas, households are more likely to use checks, invest less in cash and more in stock, have higher access to institutional credit, and make less use of informal credit. The effect of social capital is stronger where legal enforcement is weaker and among less educated people. These results are not driven by omitted environmental variables, since we show that the behavior of movers is still affected by the level of social capital of the province where they were born.
TL;DR: In this paper, the authors outline the goals of design research and how it is related to other methodologies, and provide guidelines for how design research can best be carried out in the future.
Abstract: The term "design experiments" was introduced in 1992, in articles by Ann Brown (1992) and Allan Collins (1992). Design experiments were developed as a way to carry out formative research to test and refine educational designs based on principles derived from prior research. More recently the term design research has been applied to this kind of work. In this article, we outline the goals of design research and how it is related to other methodologies. We illustrate how design research is carried out with two very different examples. And we provide guidelines for how design research can best be carried out in the future.
University of Pennsylvania1, New York University2, Princeton University3, Drexel University4, Ohio State University5, University of Chicago6, Johns Hopkins University7, University of Pittsburgh8, University of Arizona9, Fermilab10, University of Colorado Boulder11, Carnegie Mellon University12, University of Hawaii13, Apache Corporation14, Massachusetts Institute of Technology15, Spanish National Research Council16, University of Sussex17, University of Tokyo18, University of Michigan19, Rochester Institute of Technology20, Pennsylvania State University21
TL;DR: In this paper, the authors employed a matrix-based method using pseudo-Karhunen-Loeve eigenmodes, producing uncorrelated minimum-variance measurements in 22 k-bands of both the clustering power and its anisotropy due to redshift-space distortions.
Abstract: We measure the large-scale real-space power spectrum P(k) by using a sample of 205,443 galaxies from the Sloan Digital Sky Survey, covering 2417 effective square degrees with mean redshift z ≈ 0.1. We employ a matrix-based method using pseudo-Karhunen-Loeve eigenmodes, producing uncorrelated minimum-variance measurements in 22 k-bands of both the clustering power and its anisotropy due to redshift-space distortions, with narrow and well-behaved window functions in the range 0.02 h Mpc-1 < k < 0.3 h Mpc-1. We pay particular attention to modeling, quantifying, and correcting for potential systematic errors, nonlinear redshift distortions, and the artificial red-tilt caused by luminosity-dependent bias. Our results are robust to omitting angular and radial density fluctuations and are consistent between different parts of the sky. Our final result is a measurement of the real-space matter power spectrum P(k) up to an unknown overall multiplicative bias factor. Our calculations suggest that this bias factor is independent of scale to better than a few percent for k < 0.1 h Mpc-1, thereby making our results useful for precision measurements of cosmological parameters in conjunction with data from other experiments such as the Wilkinson Microwave Anisotropy Probe satellite. The power spectrum is not well-characterized by a single power law but unambiguously shows curvature. As a simple characterization of the data, our measurements are well fitted by a flat scale-invariant adiabatic cosmological model with h Ωm = 0.213 ± 0.023 and σ8 = 0.89 ± 0.02 for L* galaxies, when fixing the baryon fraction Ωb/Ωm = 0.17 and the Hubble parameter h = 0.72; cosmological interpretation is given in a companion paper.
TL;DR: Genetic and biochemical analyses of the secretory pathway have produced a detailed picture of the molecular mechanisms involved in selective cargo transport between organelles, including Vesicle budding and cargo selection, which depend on a machinery that includes the SNARE proteins.
TL;DR: In this article, the authors propose a prescriptive savings program, called Save More Tomorrow (hereafter, the SMarT program), where people commit in advance to allocating a portion of their future salary increases toward retirement savings.
Abstract: As firms switch from defined-benefit plans to defined-contribution plans, employees bear more responsibility for making decisions about how much to save. The employees who fail to join the plan or who participate at a very low level appear to be saving at less than the predicted life cycle savings rates. Behavioral explanations for this behavior stress bounded rationality and self-control and suggest that at least some of the low-saving households are making a mistake and would welcome aid in making decisions about their saving. In this paper, we propose such a prescriptive savings program, called Save More Tomorrow (hereafter, the SMarT program). The essence of the program is straightforward: people commit in advance to allocating a portion of their future salary increases toward retirement savings. We report evidence on the first three implementations of the SMarT program. Our key findings, from the first implementation, which has
TL;DR: This paper used data from a four-year experiment in which teachers and students were randomly assigned to classes to estimate teacher effects on student achievement, and found that teacher effects are estimated as between-teacher (but within-school) variance components of achievement status and residualized achievement gains.
Abstract: It is widely accepted that teachers differ in their effectiveness, yet the empirical evidence regarding teacher effectiveness is weak. The existing evidence is mainly drawn from econometric studies that use covariates to attempt to control for selection effects that might bias results. We use data from a four-year experiment in which teachers and students were randomly assigned to classes to estimate teacher effects on student achievement. Teacher effects are estimated as between-teacher (but within-school) variance components of achievement status and residualized achievement gains. Our estimates of teacher effects on achievement gains are similar in magnitude to those of previous econometric studies, but we find larger effects on mathematics achievement than on reading achievement. The estimated relation of teacher experience with student achievement gains is substantial, but is statistically significant only for 2nd-grade reading and 3rd-grade mathematics achievement. We also find much larger teacher e...
TL;DR: This article showed that the import of new product varieties has contributed to national welfare gains in the United States over the last three decades (1972-2001) by increasing the number of imported product varieties by a factor of four.
Abstract: Since the seminal work of Krugman (1979), product variety has played a central role in models of trade and growth. In spite of the general use of love-of-variety models, there has been no systematic study of how the import of new varieties has contributed to national welfare gains in the United States. In this paper we show that the unmeasured growth in product variety from US imports has been an important source of gains from trade over the last three decades (1972-2001). Using extremely disaggregated data, we show that the number of imported product varieties has increased by a factor of four. We also estimate the elasticities of substitution for each available category at the same level of aggregation, and describe their behavior across time and SITC-5 industries. Using these estimates we develop an exact price index and find that the upward bias in the conventional import price index is approximately 1.2 percent per year. The magnitude of this bias suggests that the welfare gains from variety growth in imports alone are 2.8 percent of GDP.
TL;DR: Corporate transparency, defined as the availability of firmspecific information to those outside publicly traded firms, has been investigated in this paper, where the authors conceptualize corporate transparency within a country as output from a multifaceted system whose components collectively produce, gather, validate and disseminate information.
Abstract: We investigate corporate transparency, defined as the availability of firmspecific information to those outside publicly traded firms. We conceptualize corporate transparency within a country as output from a multifaceted system whose components collectively produce, gather, validate, and disseminate information. We factor analyze a range of measures capturing countries’ firmspecific information environments, isolating two distinct factors. The first factor, interpreted as financial transparency, captures the intensity and timeliness of financial disclosures, and their interpretation and dissemination by analysts and the media. The second factor, interpreted as governance transparency, captures the intensity of governance disclosures used by outside investors to hold officers and directors accountable. We investigate whether these factors vary with countries’ legal/judicial regimes and political economies. Our main multivariate result is that the governance transparency factor is primarily related to a country’s legal/judicial regime, whereas the financial transparency factor is primarily related to political economy.
TL;DR: It is suggested that activation of the Akt oncogene is sufficient to stimulate the switch to aerobic glycolysis characteristic of cancer cells and that Akt activity renders cancer cells dependent on aerobic glyCOlysis for continued growth and survival.
Abstract: Cancer cells frequently display high rates of aerobic glycolysis in comparison to their nontransformed counterparts, although the molecular basis of this phenomenon remains poorly understood. Constitutive activity of the serine/threonine kinase Akt is a common perturbation observed in malignant cells. Surprisingly, although Akt activity is sufficient to promote leukemogenesis in nontransformed hematopoietic precursors and maintenance of Akt activity was required for rapid disease progression, the expression of activated Akt did not increase the proliferation of the premalignant or malignant cells in culture. However, Akt stimulated glucose consumption in transformed cells without affecting the rate of oxidative phosphorylation. High rates of aerobic glycolysis were also identified in human glioblastoma cells possessing but not those lacking constitutive Akt activity. Akt-expressing cells were more susceptible than control cells to death after glucose withdrawal. These data suggest that activation of the Akt oncogene is sufficient to stimulate the switch to aerobic glycolysis characteristic of cancer cells and that Akt activity renders cancer cells dependent on aerobic glycolysis for continued growth and survival.
TL;DR: This work used chromatin immunoprecipitation combined with promoter microarrays to identify systematically the genes occupied by the transcriptional regulators HNF1α, HNF4α, and HNF6, together with RNA polymerase II, in human liver and pancreatic islets.
Abstract: The transcriptional regulatory networks that specify and maintain human tissue diversity are largely uncharted. To gain insight into this circuitry, we used chromatin immunoprecipitation combined with promoter microarrays to identify systematically the genes occupied by the transcriptional regulators HNF1α, HNF4α, and HNF6, together with RNA polymerase II, in human liver and pancreatic islets. We identified tissue-specific regulatory circuits formed by HNF1α, HNF4α, and HNF6 with other transcription factors, revealing how these factors function as master regulators of hepatocyte and islet transcription. Our results suggest how misregulation of HNF4α can contribute to type 2 diabetes.
TL;DR: In this paper, brain morphology of 26 chronic back pain patients to matched control subjects was compared using magnetic resonance imaging brain scan data and automated analysis techniques, using voxel-based morphometry and nonparametric statistics.
Abstract: The role of the brain in chronic pain conditions remains speculative. We compared brain morphology of 26 chronic back pain (CBP) patients to matched control subjects, using magnetic resonance imaging brain scan data and automated analysis techniques. CBP patients were divided into neuropathic, exhibiting pain because of sciatic nerve damage, and non-neuropathic groups. Pain-related characteristics were correlated to morphometric measures. Neocortical gray matter volume was compared after skull normalization. Patients with CBP showed 5-11% less neocortical gray matter volume than control subjects. The magnitude of this decrease is equivalent to the gray matter volume lost in 10-20 years of normal aging. The decreased volume was related to pain duration, indicating a 1.3 cm3 loss of gray matter for every year of chronic pain. Regional gray matter density in 17 CBP patients was compared with matched controls using voxel-based morphometry and nonparametric statistics. Gray matter density was reduced in bilateral dorsolateral prefrontal cortex and right thalamus and was strongly related to pain characteristics in a pattern distinct for neuropathic and non-neuropathic CBP. Our results imply that CBP is accompanied by brain atrophy and suggest that the pathophysiology of chronic pain includes thalamocortical processes.
TL;DR: In this article, the authors study the effects of differences in local financial development within an integrated financial market and construct a new indicator of financial development by estimating a regional effect on the probability that, ceteris paribus, a household is shut off from the credit market.
Abstract: We study the effects of differences in local financial development within an integrated financial market. We construct a new indicator of financial development by estimating a regional effect on the probability that, ceteris paribus, a household is shut off from the credit market. By using this indicator, we find that financial development enhances the probability an individual starts his own business, favors entry of new firms, increases competition, and promotes growth. As predicted by theory, these effects are weaker for larger firms, which can more easily raise funds outside of the local area. These effects are present even when we instrument our indicator with the structure of the local banking markets in 1936, which, because of regulatory reasons, affected the supply of credit in the following 50 years. Overall, the results suggest local financial development is an important determinant of the economic success of an area even in an environment where there are no frictions to capital movements.
TL;DR: For example, this paper argued that the common elements of common moral beliefs in different cultures arise from similar problems (e.g., how to divide power and resources, care for children, and resolve disputes) for which they have often developed similar solutions.
Abstract: maps embellished with fantastical beasts, sixteenth-century wonder chambers 1⁄2lled with natural and technological marvels, even late-twentieth-century supermarket tabloids–all attest to the human fascination with things that violate our basic ideas about reality. The study of morality and culture is therefore an intrinsically fascinating topic. People have created moralities as divergent as those of Nazis and Quakers, headhunters and Jains. And yet, when we look closely at the daily lives of people in divergent cultures, we can 1⁄2nd elements that arise in nearly all of them– for example, reciprocity, loyalty, respect for (some) authority, limits on physical harm, and regulation of eating and sexuality. What are we to make of this pattern of similarity within profound difference? Social scientists have traditionally taken two approaches. The empiricist approach posits that moral knowledge, moral beliefs, moral action, and all the other stuff of morality are learned in childhood. There is no moral faculty or moral anything else built into the human mind, although there may be some innate learning mechanisms that enable the acquisition of later knowledge. To the extent that there are similarities across cultures, they arise because all cultures face similar problems (e.g., how to divide power and resources, care for children, and resolve disputes) for which they have often developed similar solutions. The nativist approach, on the other hand, holds that knowledge about such issues as fairness, harm, and respect for authority has been built into the human mind by evolution. All children who are raised in a reasonable environment will come to develop these ideas, even if they are not taught by adults. To the extent that there are differences across cultures, they arise because of local variation in the implementation of universal moral
University of Pittsburgh1, State Street Corporation2, University of Chicago3, Monash University4, University of California, Irvine5, University of Maryland, College Park6, Dalhousie University7, University of California, Santa Barbara8, University of Akron9, Washington State University10, Duke University11
TL;DR: A change in approach is needed to determine whether pollen limitation reflects random fluctuations around a pollen–resource equilibrium, an adaptation to stochastic pollination environments, or a chronic syndrome caused by an environmental perturbation.
Abstract: Determining whether seed production is pollen limited has been an area of intensive empirical study over the last two decades. Yet current evidence does not allow satisfactory assessment of the causes or consequences of pollen limitation. Here, we critically evaluate existing theory and issues concerning pollen limitation. Our main conclusion is that a change in approach is needed to determine whether pollen limitation reflects random fluctuations around a pollen–resource equilibrium, an adaptation to stochastic pollination environments, or a chronic syndrome caused by an environmental perturbation. We formalize and extend D. Haig and M. Westoby's conceptual model, and illustrate its use in guiding research on the evolutionary consequences of pollen limitation, i.e., whether plants evolve or have evolved to ameliorate pollen limitation. This synthesis also reveals that we are only beginning to understand when and how pollen limitation at the plant level translates into effects on plant population dynamics...
Kevork N. Abazajian1, Jennifer K. Adelman-McCarthy2, Marcel A. Agüeros3, Sahar S. Allam4 +162 more•Institutions (41)
TL;DR: The second data release of the Sloan Digital Sky Survey (SDSS) as mentioned in this paper is the most recent data set to be publicly available, which consists of 3.5 million unique objects, 367,360 spectra of galaxies, quasars, stars, and calibrating blank sky patches selected over 2627 deg2 of this area.
Abstract: The Sloan Digital Sky Survey (SDSS) has validated and made publicly available its Second Data Release. This data release consists of 3324 deg2 of five-band (ugriz) imaging data with photometry for over 88 million unique objects, 367,360 spectra of galaxies, quasars, stars, and calibrating blank sky patches selected over 2627 deg2 of this area, and tables of measured parameters from these data. The imaging data reach a depth of r ≈ 22.2 (95% completeness limit for point sources) and are photometrically and astrometrically calibrated to 2% rms and 100 mas rms per coordinate, respectively. The imaging data have all been processed through a new version of the SDSS imaging pipeline, in which the most important improvement since the last data release is fixing an error in the model fits to each object. The result is that model magnitudes are now a good proxy for point-spread function magnitudes for point sources, and Petrosian magnitudes for extended sources. The spectroscopy extends from 3800 to 9200 A at a resolution of 2000. The spectroscopic software now repairs a systematic error in the radial velocities of certain types of stars and has substantially improved spectrophotometry. All data included in the SDSS Early Data Release and First Data Release are reprocessed with the improved pipelines and included in the Second Data Release. Further characteristics of the data are described, as are the data products themselves and the tools for accessing them.
TL;DR: A20 was required for the termination of Toll-like receptor–induced activity of the transcription factor NF-κB and proinflammatory gene expression in macrophages, and this function protected mice from endotoxic shock, indicating that A20 is also critical for the regulation of TNF-independent signals in vivo.
Abstract: A20 is a cytoplasmic protein required for the termination of tumor necrosis factor (TNF)-induced signals. We show here that mice doubly deficient in either A20 and TNF or A20 and TNF receptor 1 developed spontaneous inflammation, indicating that A20 is also critical for the regulation of TNF-independent signals in vivo. A20 was required for the termination of Toll-like receptor-induced activity of the transcription factor NF-kappaB and proinflammatory gene expression in macrophages, and this function protected mice from endotoxic shock. A20 accomplished this biochemically by directly removing ubiquitin moieties from the signaling molecule TRAF6. The critical function of this deubiquitinating enzyme in the restriction of TLR signals emphasizes the importance of the regulation of ubiquitin conjugation in innate immune cells.
University of Tennessee Health Science Center1, University of Washington2, Creighton University3, George Mason University4, Semmelweis University5, University of Arkansas System6, University of Murcia7, Neuroscience Research Australia8, University of South Florida9, University of California, Irvine10, University of Auckland11, Johns Hopkins University12, City University of New York13, Ruhr University Bochum14, California State University, Long Beach15, Oregon Health & Science University16, St. John's University17, University of California, Los Angeles18, Bowling Green State University19, Duke University20, Newcastle University21, University of Chicago22
TL;DR: The standard nomenclature that has been used for many telencephalic and related brainstem structures in birds is reviewed, with a rationale for each name change and evidence for any homologies implied by the new names.
Abstract: The standard nomenclature that has been used for many telencephalic and related brainstem structures in birds is based on flawed assumptions of homology to mammals. In particular, the outdated terminology implies that most of the avian telencephalon is a hypertrophied basal ganglia, when it is now clear that most of the avian telencephalon is neurochemically, hodologically, and functionally comparable to the mammalian neocortex, claustrum, and pallial amygdala (all of which derive from the pallial sector of the developing telencephalon). Recognizing that this promotes misunderstanding of the functional organization of avian brains and their evolutionary relationship to mammalian brains, avian brain specialists began discussions to rectify this problem, culminating in the Avian Brain Nomenclature Forum held at Duke University in July 2002, which approved a new terminology for avian telencephalon and some allied brainstem cell groups. Details of this new terminology are presented here, as is a rationale for each name change and evidence for any homologies implied by the new names. Revisions for the brainstem focused on vocal control, catecholaminergic, cholinergic, and basal ganglia-related nuclei. For example, the Forum recognized that the hypoglossal nucleus had been incorrectly identified as the nucleus intermedius in the Karten and Hodos (1967) pigeon brain atlas, and what was identified as the hypoglossal nucleus in that atlas should instead be called the supraspinal nucleus. The locus ceruleus of this and other avian atlases was noted to consist of a caudal noradrenergic part homologous to the mammalian locus coeruleus and a rostral region corresponding to the mammalian A8 dopaminergic cell group. The midbrain dopaminergic cell group in birds known as the nucleus tegmenti pedunculopontinus pars compacta was recognized as homologous to the mammalian substantia nigra pars compacta and was renamed accordingly; a group of gamma-aminobutyric acid (GABA)ergic neurons at the lateral edge of this region was identified as homologous to the mammalian substantia nigra pars reticulata and was also renamed accordingly. A field of cholinergic neurons in the rostral avian hindbrain was named the nucleus pedunculopontinus tegmenti, whereas the anterior nucleus of the ansa lenticularis in the avian diencephalon was renamed the subthalamic nucleus, both for their evident mammalian homologues. For the basal (i.e., subpallial) telencephalon, the actual parts of the basal ganglia were given names reflecting their now evident homologues. For example, the lobus parolfactorius and paleostriatum augmentatum were acknowledged to make up the dorsal subdivision of the striatal part of the basal ganglia and were renamed as the medial and lateral striatum. The paleostriatum primitivum was recognized as homologous to the mammalian globus pallidus and renamed as such. Additionally, the rostroventral part of what was called the lobus parolfactorius was acknowledged as comparable to the mammalian nucleus accumbens, which, together with the olfactory tubercle, was noted to be part of the ventral striatum in birds. A ventral pallidum, a basal cholinergic cell group, and medial and lateral bed nuclei of the stria terminalis were also recognized. The dorsal (i.e., pallial) telencephalic regions that had been erroneously named to reflect presumed homology to striatal parts of mammalian basal ganglia were renamed as part of the pallium, using prefixes that retain most established abbreviations, to maintain continuity with the outdated nomenclature. We concluded, however, that one-to-one (i.e., discrete) homologies with mammals are still uncertain for most of the telencephalic pallium in birds and thus the new pallial terminology is largely devoid of assumptions of one-to-one homologies with mammals. The sectors of the hyperstriatum composing the Wulst (i.e., the hyperstriatum accessorium intermedium, and dorsale), the hyperstriatum ventrale, the neostriatum, and the archistriatum have been renamed (respectively) the hyperpallium (hypertrophied pallium), the mesopallium (middle pallium), the nidopallium (nest pallium), and the arcopallium (arched pallium). The posterior part of the archistriatum has been renamed the posterior pallial amygdala, the nucleus taeniae recognized as part of the avian amygdala, and a region inferior to the posterior paleostriatum primitivum included as a subpallial part of the avian amygdala. The names of some of the laminae and fiber tracts were also changed to reflect current understanding of the location of pallial and subpallial sectors of the avian telencephalon. Notably, the lamina medularis dorsalis has been renamed the pallial-subpallial lamina. We urge all to use this new terminology, because we believe it will promote better communication among neuroscientists. Further information is available at http://avianbrain.org
Ohio State University1, University of Alabama at Birmingham2, University of Texas Southwestern Medical Center3, National Institutes of Health4, George Washington University5, University of Utah6, University of Chicago7, University of Pittsburgh8, Wake Forest University9, Thomas Jefferson University10, Wayne State University11, University of Cincinnati12, Columbia University13, Brown University14, Northwestern University15, University of Miami16, University of Tennessee Health Science Center17, University of Texas at San Antonio18, University of North Carolina at Chapel Hill19, University of Texas at Austin20, Case Western Reserve University21, Vanderbilt University22
TL;DR: The proportion of women who attempt vaginal delivery after prior cesarean delivery has decreased largely because of concern about safety, and the absolute and relative risks associated with a trial of labor in women with a history of cesAREan delivery are uncertain.
Abstract: background The proportion of women who attempt vaginal delivery after prior cesarean delivery has decreased largely because of concern about safety The absolute and relative risks associated with a trial of labor in women with a history of cesarean delivery, as compared with elective repeated cesarean delivery without labor, are uncertain
TL;DR: It is found that rice (Oryza sativa) has nearly twice as many RLK/Pelle members as Arabidopsis does, and it is not simply a consequence of a larger predicted gene number in rice.
Abstract: Receptor-like kinases (RLKs) belong to the large RLK/Pelle gene family, and it is known that the Arabidopsis thaliana genome contains >600 such members, which play important roles in plant growth, development, and defense responses. Surprisingly, we found that rice (Oryza sativa) has nearly twice as many RLK/Pelle members as Arabidopsis does, and it is not simply a consequence of a larger predicted gene number in rice. From the inferred phylogeny of all Arabidopsis and rice RLK/Pelle members, we estimated that the common ancestor of Arabidopsis and rice had >440 RLK/Pelles and that large-scale expansions of certain RLK/Pelle members and fusions of novel domains have occurred in both the Arabidopsis and rice lineages since their divergence. In addition, the extracellular domains have higher nonsynonymous substitution rates than the intracellular domains, consistent with the role of extracellular domains in sensing diverse signals. The lineage-specific expansions in Arabidopsis can be attributed to both tandem and large-scale duplications, whereas tandem duplication seems to be the major mechanism for recent expansions in rice. Interestingly, although the RLKs that are involved in development seem to have rarely been duplicated after the Arabidopsis–rice split, those that are involved in defense/disease resistance apparently have undergone many duplication events. These findings led us to hypothesize that most of the recent expansions of the RLK/Pelle family have involved defense/resistance-related genes.